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Weight loss, in the context of medicine, health or physical fitness, is a reduction of the total body mass, due to a mean loss of fluid, body fat or adipose tissue and/or lean mass, namely bone mineral deposits, muscle, tendon and other connective tissue. It can occur unintentionally due to an underlying disease or can arise from a conscious effort to improve an actual or perceived overweight or obese state.

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Unintentional weight loss

Unintentional weight loss occurs in many diseases and conditions,including some very serious diseases such as cancer, AIDS, and a variety of other diseases.

Poor management of type 1 diabetes mellitus, also known as insulin-dependent diabetes mellitus (IDDM), leads to an excessive amount of glucose and an insufficient amount of insulin in the bloodstream. This triggers the release of triglycerides from adipose (fat) tissue and catabolism (breakdown) of amino acids in muscle tissue. This results in a loss of both fat and lean mass, leading to a significant reduction in total body weight. Note that untreated type 1 diabetes mellitus will usually not produce weight loss, as these patients get acutely ill before they would have had time to lose weight.

In addition to weight loss due to a reduction in fat and lean mass, illnesses such as diabetes, certain medications, lack of fluid intake and other factors can trigger fluid loss. And fluid loss in addition to a reduction in fat and lean mass exacerbates the risk for cachexia.

Infections such as HIV may alter metabolism, leading to weight loss.[1]

Hormonal disruptions, such as an overactive thyroid (hyperthyroidism), may also exhibit as weight loss.[2]

Recent research has shown fidgeting to result in significant weight loss.[3]

Causes of unintentional weight loss

Cancer, a very common and sometimes fatal cause of unexplained (idiopathic) weight loss. About one-third of unintentional weight loss cases are secondary to malignancy. Cancers to suspect in patients with unexplained weight loss include gastrointestinal, prostate, hepatobillary (hepatocellular carcinoma, pancreatic cancer), ovarian, hematologic or lung malignancies should be considered in any patient presenting with unexplained weight loss.

AIDS can cause weight loss and should be suspected in high-risk individuals presenting with weight loss.

Gastrointestinal disorders are another common cause of unexplained weight loss - in fact they are the most common non-cancerous cause of idiopathic weight loss. Possible gastrointestinal etiologies of unexplained weight loss are celiac disease, a fairly common and well-known disease caused by intolerance of gluten, peptic ulcer, inflammatory bowel disease (crohns disease and ulcerative colitis), pancreatitis, gastritis, diarrhea and many other GI conditions can cause weight loss.

Infection. Some infectious diseases can cause weight loss. These include fungal illness, endocarditis, many parasitic diseases, AIDS, and some other sub-acute or occult infections may cause weight loss.

Renal disease. Patients who have uremia often have poor or absent appetite, emesis and nausea. This can cause weight loss.

Attention to diet in particular can be extremely beneficial in reducing the impact of diabetes and other health risks of an expanding waist.

Weight loss occurs when an individual is in a state of negative energy balance. When the body is consuming more energy (i.e. in work and heat) than it is gaining (i.e. from food or other nutritional supplements), it will use stored reserves from fat or muscle, gradually leading to weight loss.[citation needed]

It is not uncommon for some people who are currently at their ideal body weight to seek additional weight loss in order to improve athletic performance, and/or meet required weight classification for participation in a sport. However, others may be driven by achieving a more attractive body image. Consequently, being underweight is associated with health risks such as difficulty fighting off infection, osteoporosis, decreased muscle strength, trouble regulating body temperature and even increased risk of death.[7]

Therapeutic weight loss techniques

The least intrusive weight loss methods, and those most often recommended, are adjustments to eating patterns and increased physical activity, generally in the form of exercise. Physicians will usually recommend that their overweight patients combine a reduction of processed[8] and caloric content of the diet with an increase in physical activity.[9]

Other methods of losing weight include use of drugs and supplements that decrease appetite, block fat absorption, or reduce stomach volume.

Weight Loss Coaching is rapidly growing in popularity in the United States, with the number of available coaches nearly doubling since 2000.[citation needed] Finally, surgery (i.e. bariatric surgery) may be used in more severe cases to artificially reduce the size of the stomach, thus limiting the intake of food energy.

Crash dieting

A crash diet refers to willful nutritional restriction (except water) for more than 12 hours. The desired result is to have the body burn fat for energy with the goal of losing a significant amount of weight in a short time. There is a possibility of excessive muscle loss, depending on the approach used.

Crash dieting is not the same as intermittent fasting, in which the individual periodically abstains from food (e.g., every other day).

Weight loss industry

There is a substantial market for products which promise to make weight loss easier, quicker, cheaper, more reliable, or less painful. These include books, CDs, cremes, lotions, pills, rings and earrings, body wraps, body belts and other materials, not to mention fitness centers, personal coaches, weight loss groups, and food products and supplements. US residents in 1992 spent an estimated $30 billion a year on all types of diet programs and products, including diet foods and drinks.[10]

Between $33 billion and $55 billion is spent annually on weight loss products and services, including medical procedures and pharmaceuticals, with weight loss centers garnering between 6 percent and 12 percent of total annual expenditure. About 70 percent of Americans' dieting attempts are of a self-help nature. Although often short-lived, these diet fads are a positive trend for this sector as Americans ultimately turn to professionals to help them meet their weight loss goals.[11]